Just taken back up riding but the old girl has seen better days. The old power index system is somewhat rusty and I am having trouble selecting and maintaining any particular gear.
Because of the age and condition of the cog assembly I wondered if there is any way I can get by until I can afford a newer bike. I'm not a mechanic but I have been known to take things apart - not always successfully.
Any advice would be appreciated
soak in pb blaster and work it to get it to loosen up, make sure your cables are moving freely in the housing.
I use ultrasonic cleaners with heated cycles filled with evapo-rust, I use another machine with degreaser that I use first
There are two kinds of people in the world, "Those who help themselves to people, and those who help people!"
Replacing the chain and the derailleur is your best option if you can't salvage what you have.
You might also need to change the shifter cable.
Evaporust does work wonders for derailleurs. I wouldn't recommend it for chains. You can just lube the derailleur after words and it's good as new basically.
You should re-index your derailleur also.
Shift into the highest gear (smallest rear cog). Undo the cable. Dial the barrel adjuster in all the way (clockwise). Slightly tug the cable to remove only the most basic slack and re-fasten the bolt. Dial out the high limit screw all the way. Look to the cassette and dial the limit screw in until your pulley is linear with the smallest cog. Begin to dial the barrel adjuster out slightly and shift up while you turn the crank. If it doesn't shift, go back down, dial the adjuster out a little more and try again. Use this method until you restore shifting performance.
If something goes wrong from here, check the b screw and dial it out first a little bit. If that doesn't help dial it in a little bit.
If something goes wrong from here, consider buying a new derailleur and/or shifter.